Each participant will be evaluated by a history and initial neurological exam. Up to another 20 mL of blood will be drawn for routine blood studies. Other medical care procedures may include a chest x-ray, EKG and echocardiogram, CT (computed tomography) or MRI (magnetic resonance imaging) scan, pulmonary function tests, and physical therapy assessment. Possible research procedures may include MR spectroscopy, nerve conduction study, electromyography, muscle or nerve biopsy, and lumbar puncture.